Ivor and Olive Lewis on thu 8 jun 06
Dear Ron,
You say, ...automatically
get more melting.
I makes sense to me but don't ask me why - I'm sure there are people =
around
who can explain why - I certainly know it's true when you sub in Li2O =
for
KNaO.>...
Perhaps it would pay us to think in slightly different terms. First, be =
clear that we must compare like with like so fix the temperature and =
make sure that this will not be raised or lowered.
If we say "more melting" then there is an implication that not all of =
the ingredients in the original recipe have changed from solid to =
liquid. Change to "Greater fluidity" and a new picture emerges which =
allows for all of the original ingredients to fully dissolve but =
decrease viscosity with the addition of a further ingredient introducing =
a new element=20
Information in the texts gives us hope when we read that incorporating =
certain fluxing agents affects Viscosity. On the face of it, it would =
appear that if Lithium Oxide (*) is substituted for K2O or Na2O there =
would be an increase in viscosity, and the glaze will not flow as =
freely. But if we augment the glaze by adding Lithium carbonate while =
retaining K2O or Na2O then we should, if the information we are given =
is true, decrease the viscosity and encourage flow. I prefer to add =
Petalite
(*) Lithium Carbonate decomposes at 1300 deg C. Lithium Monoxide melts =
at 1700 deg C. Lepidolite decomposes at 1200 deg C, Petalite melts at =
1300 deg C, Spodumene melts at 1400 deg C.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on sat 10 jun 06
Hi Ivor,
Yes - of course - start with a glaze that can be melted more - how else
would you know if there was more melting?
Surely someone has done the experiments - just a matter if finding the results.
I would not use Lithium Carb. - but rather spodumene - which as almost
twice as much Li2O as petalite - you have lots of spod there - or is the
mine closed?
The decomposition temp of Lithium carbonate is 650C by the way - or it
would not work as a flux in even low fired glazes. The other numbers are
the same as in Hamers appendix.
RR
>You say, ...>automatically
>get more melting.
>I makes sense to me but don't ask me why - I'm sure there are people around
>who can explain why - I certainly know it's true when you sub in Li2O for
>KNaO.>...
>
>Perhaps it would pay us to think in slightly different terms. First, be
>clear that we must compare like with like so fix the temperature and make
>sure that this will not be raised or lowered.
>
>If we say "more melting" then there is an implication that not all of the
>ingredients in the original recipe have changed from solid to liquid.
>Change to "Greater fluidity" and a new picture emerges which allows for
>all of the original ingredients to fully dissolve but decrease viscosity
>with the addition of a further ingredient introducing a new element
>
>Information in the texts gives us hope when we read that incorporating
>certain fluxing agents affects Viscosity. On the face of it, it would
>appear that if Lithium Oxide (*) is substituted for K2O or Na2O there
>would be an increase in viscosity, and the glaze will not flow as freely.
>But if we augment the glaze by adding Lithium carbonate while retaining
>K2O or Na2O then we should, if the information we are given is true,
>decrease the viscosity and encourage flow. I prefer to add Petalite
>
>(*) Lithium Carbonate decomposes at 1300 deg C. Lithium Monoxide melts at
>1700 deg C. Lepidolite decomposes at 1200 deg C, Petalite melts at 1300
>deg C, Spodumene melts at 1400 deg C.
>
>Best regards,
>
>Ivor Lewis.
>Redhill,
>South Australia.
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on sun 11 jun 06
Dear Ron,
Why must it be true that Lithium Carbonate decomposes at 650 C ?
To be sure of your sources you need to check Hamers References. Where
does his information come from ? Just how good is it ? I have a 1s.t
.Ed. He gives Uvarov and Isaacs as a scientific text reference but
they do not say anything about Li2CO3 decomposing
For the best factual information I would back Kaye and Laby, produced
by the National Physical Laboratory in the UK or The CRC Handbook
printed in the US any day when it comes to fine details. I think K & L
cost me about $Au 60:00 back in the 1980's and I got a Student version
of CRC handbook a few of years ago for a mere $Au 150:00. This is an
amazing book. Great for weight training ! !
The Ellingham diagram shows that Lithium Oxide is exceptionally stable
under the influence of heat with a sublimation point at 1310 deg C
(1583 K) at 1 bar. No low temperature melting ! ! Melting point is
given as being in the region of 1700 C but that must be under
pressure. Hardly the credentials for a "Fluxing Oxide" when it changes
directly form solid to vapour.
Regarding Metallic Carbonates P. J. Durrant in "General and Inorganic
Chemistry" writes "The Carbonates of all metals other than those of
the alkali metals and Barium are decomposed by heat. Lithium carbonate
is similarly decomposed with some difficulty. As I have written
before, the temperature given is 1310 C. But it does melts at 723 C. A
question to ask is "When molten, does it dissolve silicate minerals".
Easy enough to do a fusion test on an platinum wire in a Bunsen flame.
Daniel Semler on sun 11 jun 06
Hi Ivor,
What you say about CRC Handbooks is definitely true though I have yet
to get a
copy myself.
On the lithium decomposition versus melting thing I can add just a little and
a question.
The 5th Ed of Hamer's reports decomposition as :
Li2OCO3 -> Li2O + CO2 occurring at 650 deg C
Oddly John Conrad, Advanced Ceramic Manual, reports 618-710 as a
melting point
in his Properties of Minerals Used in Ceramics table. He marks decomposition
temps with a "D". Thus one would conclude that he does not consider this a
decomposition temp. as its not so marked. I don't have another source for the
decomposition temp of Li2OCO3. I was just looking on the web and it seems that
some sources quote 600ish as in this data sheet
and
others say 1310.
So my question is if it melts before it decomposes how does that work ? Does
it go from solid lithium carb. to liquid lithium carb. at 650 ish and then we
could get the liquid to decompose at 1310 deg C ? Is this remotely
close to the
mark ? I'm trying to understand how this behaves. Of course this is without
considering other effects, such as the dissolving of the lithium carbonate in
any existing melt at the time.
I found one reference stating it could decompose at about 800 deg C in the
presence of a hydrogen atmosphere but no real explanation.
Thx
D
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